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SocialPhotographer
SocialPhotographer
Participating Frequently
October 7, 2023
質問

Photoshop : trouble subtracting one layer mask from another

  • October 7, 2023
  • 返信数 3.
  • 7150 ビュー

Hi everyone, I'm having trouble subtracting one layer mask from another. 

 

I have a complex background mask on its own layer. The background mask includes some of the subjects. I would like to subtract the subject layer masks, one at a time, from the background mask. 

 

I used "select subject" to create multiple empty groups, each group having a layer mask revealing one of the subjects.

I tried to follow Julieanne Kost's blog post instructions--

 

Converting a Layer Mask into a Selection

To convert a Layer Mask to a selection, Command -click (Mac) | Control -click (Win) on the Layer Mask thumbnail in the Layers panel. You can then add, subtract or intersect the resulting selection with another Layer Mask using the following shortcuts:
Command + Shift (Mac) | Control + Shift (Win) to add additional Layer Mask to the selection.
Option +Command (Mac) | Alt +Control (Win) to subtract another Layer Mask from the selection.
Option +Command + Shift (Mac) | Alt +Control + Shift (Win) to create the intersection of two Layer Masks.

https://jkost.com/blog/2017/08/15-shortcuts-for-working-with-layer-masks-in-photoshop-cc.html

 

--- with no success. What happens is as follows, in Photoshop 25.0.0--

  1.  Converting the target layer mask (the background mask) to a selection is successful.
  2.  When I press and hold Alt + Ctrl, the cursor shows a minus sign for subtraction : successful
  3.  Still holding down Alt + Ctrl, when I left-click on the subject mask in the other group layer, to subtract the subject from the background, a blue border briefly flashes around the Layers panel, and the subject layer mask is selected, while the target background layer mask is deselected. Not what I intended.

4. I also tested adding the subject mask to the background mask, as well as intersecting. Both of these operations work successfully, per instructions above.

 

I also tested and verified my Ctrl and Alt keys ((Logitech MX Keys), and Alt + Ctrl, using Windows 10 On-Screen Keyboard.

 

As a workaround, I'm wondering if the layer mask subtraction can be performed by "promoting" the 2 layer masks to first-class greyscale images, on separate layers, and then using a blend mode and flatten?


Any help sincerely appreciated, please?
Thank you for your consideration.

    このトピックへの返信は締め切られました。

    返信数 3

    Semaphoric
    Community Expert
    SemaphoricCommunity Expert
    Community Expert
    October 8, 2023

    I would save all your masks as individual alpha channels, and use Image > Calculations to do the math.

      Stephen Marsh
      Community Expert
      Stephen MarshCommunity Expert
      Community Expert
      October 9, 2023
      quote

      I would save all your masks as individual alpha channels, and use Image > Calculations to do the math.


      By @Semaphoric

       

      I was going to suggest Apply Image, either way, the same idea, working with pixel data rather than selections.

      Trevor.Dennis
      Community Expert
      Trevor.DennisCommunity Expert
      Community Expert
      October 9, 2023

      I had to look up how that would work Stephen, and found a cool feature I have never used before.  You never stop learning with Photoshop.

       

      Trevor.Dennis
      Community Expert
      Trevor.DennisCommunity Expert
      Community Expert
      October 7, 2023

      Make the layer with its mask a Smart Object and add another layer mask.

      SocialPhotographer
      SocialPhotographer作成者
      Participating Frequently
      October 7, 2023

      Hi Trevor, thank you for responding and for your suggestion. Just for everyone's benefit, Julieanne Kost has a YouTube video on the technique you described.

      I tested this out on my end, and I got the intersection of the 2 masks, not the subtractive difference I'm looking for.

      Trevor.Dennis
      Community Expert
      Trevor.DennisCommunity Expert
      Community Expert
      October 8, 2023

      I am not completely sure of you entire intended workflow, but I think you might be able to get it from this.

       

      Assuming you have two layers with overlapping layer masks.

      Ctrl click the first layer mask to load it as a selection, and use Make work path from selection icon in the Paths panel.  Repeat for the other channel.

       

      Ctrl click the layer 2 path to make ALL OF its points active, and copy with Ctrl c

      Select layer 1's path, and paste with Ctrl v

      You can now use the Path Operations drop down in the Option Bar, and select the required interaction.

       

      I am sure you can work it out from there.  I'd probabl;y delete the existing mask from layer 1. Ctrl click the layer on path tp load as a selection, and re-add a layer mask to layer 1

      SocialPhotographer
      SocialPhotographer作成者
      Participating Frequently
      October 7, 2023

      Another workaround I'll try is working the other way, and adding subject masks to a new black layer mask.

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